Engine rotation can be stopped in a variety of ways to achieve a variety of results. In one example, an electric motor coupled to the engine can be used to control stopping position along with compression energy stored in the compressed gas in the cylinder. Specifically, electric motor control either before or after the engine stops can be used, or mechanically re-designing the engine may be used.
However, the inventors herein have recognized some issues with such an approach. For example, some vehicles may not be equipped with a motor or electrical storage system than can reliably perform the desired torque control before the engine stops. Further, as operating conditions vary, the amount of compression force available can vary, thus affecting the stop position greatly.
Thus, in one approach, a method for operating at least an intake and exhaust valve in a cylinder with a piston of an engine in a vehicle is provided. The method comprises: during conditions of an engine shut-down, monitoring engine rotation; and when engine speed falls below a threshold value, adjusting one of an intake or exhaust valve opening or closing to repeatably stop the engine with a selected piston in a selected location.
In this way, it is possible to obtain repeatable engine stopping control without requiring additional motor operation (although such operation may be used, if desired). Further, valve adjustments can be made to reduce oxygen flowing to the exhaust to improve catalyst operation on subsequent restarts.